The present invention relates generally to the field of electron beam lithography and more particularly to an electron beam lithography apparatus having a contamination reducing bypass valve.
The need to continually reduce feature size is ongoing in the manufacture of semiconductor integrated circuits. This need creates a corresponding need to produce masks used in optical and x-ray lithography having continually decreasing feature sizes defined thereon. Electron beam lithography systems have been used for many years to manufacture such masks. One such system is the EL5 Electron Beam Lithography System manufactured by International Business Machines Corporation. The inventors have recognized that the electron beam column in such systems contains many elements, such as shaping apertures, typically made of gold foil, which are fragile and highly sensitive to contamination. The inventors have recognized that sources of contamination include (i) resist vapor created during the exposure of a mask in the process chamber of the electron beam lithography apparatus under high vacuum and (ii) particulates which are transported through the system during pump down of the apparatus to achieve a high vacuum process environment and venting of the apparatus chambers to return the environment to atmospheric pressure.
Accordingly an electron beam lithography apparatus is provided having a first chamber for holding a workpiece with the first chamber having an outer wall with an opening therein. The apparatus further includes a second chamber having an electron beam column mounted therein, with the second chamber positioned adjacent the first chamber and having an outer wall having a portion in common with the portion of the outer wall of the first chamber containing the opening. An electron beam column in the second chamber includes an aperture and generates an electron beam through the aperture and the opening at the workpiece. The apparatus further includes a first pump for creating a vacuum in the first chamber, a second pump for creating a vacuum in the second chamber, a first vent for permitting gas to enter the first chamber for increasing the pressure in the first chamber, and a second vent for permitting gas to enter the second chamber for increasing the pressure in the second chamber. The apparatus further includes a balancing bypass valve in the common wall between the first and second chambers for (i) operating in a first mode to permit gases to flow from the first chamber to the second chamber when the pressure in said second chamber exceeds the pressure in the first chamber, (ii) operating in a second mode to permit gases to flow from the second chamber to the first chamber when the pressure in the first chamber exceeds the pressure in the second chamber, and (iii) operating in a third mode to seal the first chamber from the second chamber when the pressures in the first and second chambers are equal.
Accordingly, a feature of the present invention is the provision of an electron beam lithography apparatus which minimizes contamination of the electron beam column components during pressure changes within the apparatus.
Another feature of the present invention is the provision of an electron beam lithography apparatus which minimizes contamination of the electron beam column in a relatively simple and cost effective manner.
Other advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
FIGS. 1A-1C show schematic diagrams depicting the operation of a prior electron beam lithography apparatus;
FIG. 2 shows a schematic diagram of the electron beam lithography apparatus of the present invention;
FIGS. 3A-3C show schematic diagrams depicting the operation of the electron beam lithography apparatus of the present invention;
FIGS. 4A-4C show schematic diagrams depicting the operation of the bypass valve shown in FIG. 2 and FIGS. 3A-3C in greater detail;
FIG. 5 shows an exploded view of a second embodiment of the bypass valve of the present invention; and
FIG. 6 shows a schematic diagram depicting the operation of the bypass valve shown in FIG. 5.